Jogging and stair climbing are recommended exercises for strengthening leg muscles and the cardiovascular system. However, physicians have concluded that in some cases jogging and stair climbing transmit substantial shock loading to bones and joints of the human body which may be injurious.
Low impact exercise equipment of the type disclosed in U.S. Pat. No. 4,838,543 incorporates a structure which is used similarly to a stationary bicycle wherein the user stands on a pair of foot beams pivotally connected to a stationary frame. Shock absorbers are connected between the stationary frame and the foot beams to resist pivotal movement of each foot beam relative to the stationary frame. A rope is connected over a pulley mounted on the stationary frame above the foot beams for elevating the end of one beam when a downward force is applied to the other beam.
U.S. Pat. No. 4,830,362 entitled "FULL BODY, SHOCK-FREE AEROBIC AND ANAEROBIC EXERCISING MACHINE FOR USE IN THE STANDING POSITION" discloses a pair of foot beams pivotally mounted to a stationary frame in combination with a pair of handle bars pivotally mounted to the frame. The foot beams and handle bars are pivotally connected by tie rods and rocker arms such that rotation of a lower foot beam on either side of the frame in one direction causes rotation of the upper handle bars on the same side of the frame in the opposite direction for synchronizing movement of the foot beams and the handle bars. The system of rocker arms and tie rods is devised to simultaneously exercise upper and lower body parts while the person exercising is in a standing position on a stationary machine.
The operation of the foot beams of each of the aforementioned patents is similar except that movement of the foot beams of one apparatus is synchronized by a rope and pulley system while a rocker arm and a pair of connecting rods synchronize the foot beams of the other system. The rocker arm pivots about a longitudinal axis. The rocker arm and connecting rods used in one of the systems are mounted below the pivot point of the foot beams such that the connecting rods connected to opposite ends of the rocker arm are loaded in compression during operation of the apparatus. Thus, the tie rods may tend to wobble as the foot beams are reciprocated in view of the arcuate movement of the respective members resulting in stress and excessive wear to bearing structures.